Electricity & Magnetism Formulas
A complete list of electricity & magnetism formulas, covering Ohm's law, electric and magnetic fields, capacitance, circuits, flux, and Faraday's law.
27 formulas. Use the interactive searcher to solve for any variable and convert units.
Open the interactive searcher →Ohm's law
V = I·R
V voltageVI currentAR resistanceΩ
Electrical power
P = V·I
P powerWV voltageVI currentA
Electrical energy
E = V·I·t
E energyJV voltageVI currentAt times
Charge
Q = I·t
Q chargeCI currentAt times
Coulomb's law
F = k·q₁·q₂ / r²
F forceNk Coulomb constantN·m²/C²q₁ chargeCq₂ chargeCr distancem
Capacitance
C = Q / V
C capacitanceFQ chargeCV voltageV
Resistivity
R = ρ·L / A
R resistanceΩρ resistivityΩ·mL lengthmA aream²
Magnetic force on wire
F = B·I·L
F forceNB magnetic fieldTI currentAL lengthm
Force on moving charge
F = q·v·B
F forceNq chargeCv velocitym/sB magnetic fieldT
Resistors in series
R_eq = R₁ + R₂ + …
R_eq equivalent resistanceΩR₁ resistanceΩR₂ resistanceΩ
Resistors in parallel
1/R_eq = 1/R₁ + 1/R₂ + …
R_eq equivalent resistanceΩR₁ resistanceΩR₂ resistanceΩ
Capacitors in parallel
C_eq = C₁ + C₂ + …
C_eq equivalent capacitanceFC₁ capacitanceFC₂ capacitanceF
Capacitors in series
1/C_eq = 1/C₁ + 1/C₂ + …
C_eq equivalent capacitanceFC₁ capacitanceFC₂ capacitanceF
Power (I²R)
P = I²·R
P powerWI currentAR resistanceΩ
Power (V²/R)
P = V² / R
P powerWV voltageVR resistanceΩ
Electric field (point charge)
E = k·q / r²
E electric fieldV/mk Coulomb constantN·m²/C²q chargeCr distancem
Electric field (force)
E = F / q
E electric fieldV/mF forceNq chargeC
Electric potential energy
U = k·q₁·q₂ / r
U potential energyJk Coulomb constantN·m²/C²q₁ chargeCq₂ chargeCr distancem
Electric potential
V = k·q / r
V electric potentialVk Coulomb constantN·m²/C²q chargeCr distancem
Capacitor energy
E = ½·C·V²
E energyJC capacitanceFV voltageV
Parallel plate capacitor
C = ε₀·A / d
C capacitanceFε₀ permittivityF/mA aream²d separationm
Drift velocity
I = n·A·q·v_d
I currentAn charge density1/m³A aream²q chargeCv_d drift velocitym/s
Magnetic flux
Φ = B·A·cosθ
Φ magnetic fluxWbB magnetic fieldTA aream²θ anglerad
Faraday's law
ε = −N·dΦ/dt
ε EMFVN number of turnsΦ magnetic fluxWbt times
Solenoid field
B = μ₀·n·I
B magnetic fieldTμ₀ permeabilityH/mn turns per length1/mI currentA
Field around wire
B = μ₀·I / (2π·r)
B magnetic fieldTμ₀ permeabilityH/mI currentAr distancem
Transformer ratio
V_s/V_p = N_s/N_p
V_s secondary voltageVV_p primary voltageVN_s secondary turnsN_p primary turns